JP4449818B2 - Catalyst deterioration judgment device - Google Patents

Description

  The present invention relates to a catalyst deterioration determination device that determines deterioration of a catalyst provided in an exhaust passage of an internal combustion engine.

  There is known an apparatus that calculates the oxygen storage capacity (OSC: Oxygen Storage Capacity) of a catalyst provided in an exhaust passage of an internal combustion engine and determines the deterioration of the catalyst based on the calculated oxygen storage capacity (for example, Patent Documents). 1). According to this device, the control target value of the air-fuel ratio (hereinafter referred to as “target air-fuel ratio”) is changed from the fuel rich side (or fuel lean side) to the fuel lean side (or fuel rich side) and then downstream of the catalyst. By calculating the oxygen excess or oxygen deficiency (hereinafter referred to as “oxygen excess / deficiency”) of the exhaust gas flowing into the catalyst during the time until the output of the oxygen sensor is reversed, the oxygen storage capacity of the catalyst is calculated. The

JP-A-6-159048 JP-A-6-129285 JP-A-5-312025

However, when the deterioration of the catalyst proceeds, there may occur a situation where the output of the oxygen sensor is reversed before the oxygen absorption / release reaction proceeds sufficiently from the center to the rear of the catalyst.
FIG. 14 is a diagram showing a temperature change associated with the oxygen storage reaction of the catalyst. FIG. 14A is a diagram showing a set state of the target air-fuel ratio, and FIG. 14B is a diagram showing a change in the oxygen sensor output. FIGS. 14C, 14D, and 14E are diagrams showing temperature changes at the front, center, and rear of the catalyst, respectively.
As shown in FIG. 14A, when the target air-fuel ratio is changed from the fuel rich value 13.8 to the fuel lean value 15.2, the oxygen storage reaction proceeds in the catalyst. The oxygen storage reaction in the catalyst is an exothermic reaction. For this reason, as the oxygen storage reaction proceeds from the front to the rear of the catalyst, first, as shown in FIG. 14C, a temperature rise peak (hereinafter abbreviated as “peak”) P1 occurs at the front of the catalyst. Next, as shown in FIG. 14 (D), a peak P2 occurs at the center of the catalyst, and thereafter, a peak P3 occurs at the rear of the catalyst as shown in FIG. 14 (E). Therefore, based on these peaks P1 to P3, it is possible to grasp to which part of the catalyst the oxygen storage reaction has proceeded.
As shown in FIG. 14E, the peak P3 does not occur at the rear portion of the catalyst at the reversal time tr of the oxygen sensor output. Therefore, it can be seen that the oxygen sensor output is reversed before the oxygen storage reaction proceeds to the rear end of the catalyst. In this case, the oxygen storage capacity of the entire catalyst cannot be calculated.
Therefore, the method for determining the deterioration of the catalyst based on the oxygen storage capacity of the catalyst cannot accurately determine the deterioration of the catalyst. Further, it is impossible to accurately detect a catalyst having a high degree of deterioration.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to determine the deterioration of a catalyst with high accuracy without being based on the oxygen storage capacity of the catalyst.

In order to achieve the above object, a first invention is a catalyst deterioration determination device for determining deterioration of a catalyst provided in an exhaust passage of an internal combustion engine,
An exhaust gas sensor that is provided downstream of the catalyst and detects whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
An air-fuel ratio control means for changing the target air-fuel ratio alternately between the fuel rich side and the fuel lean side in a cycle shorter than the cycle in which the oxygen storage capacity of a normal catalyst fails;
Catalyst deterioration determination means for determining that the catalyst has deteriorated when the exhaust gas sensor detects that the air-fuel ratio is on the fuel lean side before a predetermined time elapses after the start of fluctuation of the target air-fuel ratio; It is characterized by having.

The second invention is a catalyst deterioration determination device for determining deterioration of a catalyst provided in an exhaust passage of an internal combustion engine,
An exhaust gas sensor that is provided downstream of the catalyst and detects whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
An air-fuel ratio control means for changing the target air-fuel ratio of the exhaust gas alternately between the fuel-rich side and the fuel-lean side at a cycle shorter than the cycle at which the oxygen storage capacity of a normal catalyst fails, Air-fuel ratio control means for gradually changing the fluctuation range of the target air-fuel ratio after a predetermined time has elapsed from the start of fluctuation;
Intake air for calculating the amount of air taken into the internal combustion engine after the change of the fluctuation range is started and until the exhaust gas sensor detects that the air-fuel ratio has changed from the fuel rich side to the fuel lean side A quantity calculation means;
And a catalyst deterioration determining means for determining deterioration of the catalyst based on the air amount calculated by the intake air amount calculating means.

A third invention is a catalyst deterioration determination device for determining deterioration of a catalyst provided in an exhaust passage of an internal combustion engine,
An exhaust gas sensor that is provided downstream of the catalyst and detects whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
An air-fuel ratio control means for changing the target air-fuel ratio of the exhaust gas alternately between the fuel-rich side and the fuel-lean side at a cycle shorter than the cycle at which the oxygen storage capacity of a normal catalyst fails, An air-fuel ratio control means for gradually changing the fluctuation range of the target air-fuel ratio after a predetermined time has elapsed from the start of the fluctuation;
Intake air amount for calculating the amount of air taken into the internal combustion engine after the start of change of the fluctuation range until the exhaust gas sensor detects that the air-fuel ratio has changed from the fuel lean side to the fuel rich side Computing means;
And a catalyst deterioration determining means for determining deterioration of the catalyst based on the air amount calculated by the intake air amount calculating means.

A fourth invention is a catalyst deterioration determination device for determining deterioration of a catalyst provided in an exhaust passage of an internal combustion engine,
An exhaust gas sensor that is provided downstream of the catalyst and detects whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
An air-fuel ratio control means for changing the target air-fuel ratio of the exhaust gas alternately between the fuel-rich side and the fuel-lean side at a cycle shorter than the cycle at which the oxygen storage capacity of a normal catalyst fails, Air-fuel ratio control means for gradually changing the fluctuation cycle of the target air-fuel ratio after a predetermined time has elapsed from the start of fluctuation;
Intake air for calculating the amount of air taken into the internal combustion engine between the start of change of the fluctuation period and the time when the exhaust gas sensor detects that the air-fuel ratio has changed from the fuel rich side to the fuel lean side A quantity calculation means;
And a catalyst deterioration determining means for determining deterioration of the catalyst based on the air amount calculated by the intake air amount calculating means.

The fifth invention is a catalyst deterioration determination device for determining deterioration of a catalyst provided in an exhaust passage of an internal combustion engine,
An exhaust gas sensor that is provided downstream of the catalyst and detects whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
An air-fuel ratio control means for changing the target air-fuel ratio of the exhaust gas alternately between the fuel-rich side and the fuel-lean side at a cycle shorter than the cycle at which the oxygen storage capacity of a normal catalyst fails, An air-fuel ratio control means for gradually changing the fluctuation cycle of the target air-fuel ratio after a predetermined time has elapsed from the start of the fluctuation;
Intake air for calculating the amount of air sucked into the internal combustion engine after the change of the fluctuation period is started and until the exhaust gas sensor detects that the air-fuel ratio has changed from the fuel lean side to the fuel rich side A quantity calculation means;
And a catalyst deterioration determining means for determining deterioration of the catalyst based on the air amount calculated by the intake air amount calculating means.

  According to a sixth aspect of the invention, in the second or fourth aspect of the invention, the catalyst deterioration determining means is configured such that when the amount of air calculated by the intake air amount calculating means is small, the amount of air is large. It is determined that the degree of deterioration of the catalyst is large.

  According to a seventh aspect of the invention, in the third or fifth aspect of the invention, the catalyst deterioration determining means has a larger amount of air calculated by the intake air amount calculating means than when the amount of air is small. It is determined that the degree of deterioration of the catalyst is large.

  According to an eighth aspect of the present invention, in the second, fourth or sixth aspect, the catalyst deterioration determining means is detected by the exhaust gas sensor after a predetermined time has elapsed since the change of the fluctuation range or fluctuation period was started. When the air-fuel ratio is on the fuel rich side, it is determined that the degree of deterioration of the catalyst is small.

  According to a ninth invention, in the third, fifth, or seventh invention, the catalyst deterioration determination means is detected by the exhaust gas sensor after a predetermined time has elapsed since the change of the fluctuation range or fluctuation period was started. When the air-fuel ratio is on the fuel lean side, it is determined that the degree of deterioration of the catalyst is large.

  According to a tenth aspect of the present invention, in any one of the first to ninth aspects, the air-fuel ratio control means varies the target air-fuel ratio centering on a value on the fuel rich side with respect to the theoretical air-fuel ratio. It is characterized by that.

  In an eleventh aspect based on any one of the first to tenth aspects, the air-fuel ratio control means sets the target air-fuel ratio when the amount of air sucked into the internal combustion engine is equal to or less than a predetermined value. It is characterized by being varied.

  According to the first invention, by changing the target air-fuel ratio in a short cycle, an environment is created in which only the oxygen storage reaction apparently proceeds in the deteriorated catalyst. Therefore, if the exhaust gas sensor detects that the air-fuel ratio is on the fuel lean side before the predetermined time elapses from the start of the change in the target air-fuel ratio, it can be determined that the catalyst has deteriorated. Therefore, it is possible to accurately determine the deterioration of the catalyst without being based on the oxygen storage capacity of the catalyst.

  According to the second invention, by gradually reducing the fluctuation range of the target air-fuel ratio, an environment in which the oxygen release reaction in the catalyst hardly occurs is created. In such an environment, the time when the air-fuel ratio downstream of the catalyst changes from the fuel rich side to the fuel lean side is detected by the exhaust gas sensor, the amount of intake air up to this point is calculated, and the catalyst air flow is calculated based on the calculated amount of intake air. Deterioration determination can be performed. Therefore, it is possible to accurately determine the deterioration of the catalyst without being based on the oxygen storage capacity of the catalyst.

  According to the third invention, by gradually increasing the fluctuation range of the target air-fuel ratio, an environment in which an oxygen release reaction is likely to occur in the catalyst is created. In such an environment, the exhaust gas sensor detects when the air-fuel ratio downstream of the catalyst changes from the fuel lean side to the fuel rich side, calculates the intake air amount up to this point, and based on the calculated intake air amount, Deterioration determination can be performed. Therefore, it is possible to accurately determine the deterioration of the catalyst without being based on the oxygen storage capacity of the catalyst.

  According to the fourth aspect of the present invention, an environment in which the oxygen release reaction hardly occurs in the catalyst is created by gradually reducing the fluctuation cycle of the target air-fuel ratio. In such an environment, the time when the air-fuel ratio downstream of the catalyst changes from the fuel rich side to the fuel lean side is detected by the exhaust gas sensor, the amount of intake air up to this point is calculated, and the catalyst air flow is calculated based on the calculated amount of intake air. Deterioration determination can be performed. Therefore, it is possible to accurately determine the deterioration of the catalyst without being based on the oxygen storage capacity of the catalyst.

  According to the fifth aspect of the invention, by gradually increasing the fluctuation cycle of the target air-fuel ratio, an environment in which an oxygen release reaction is likely to occur in the catalyst is created. In such an environment, the exhaust gas sensor detects when the air-fuel ratio downstream of the catalyst changes from the fuel lean side to the fuel rich side, calculates the intake air amount up to this point, and based on the calculated intake air amount, Deterioration determination can be performed. Therefore, it is possible to accurately determine the deterioration of the catalyst without being based on the oxygen storage capacity of the catalyst.

  According to the sixth and seventh aspects, it is possible to accurately determine the degree of deterioration of the catalyst based on the intake air amount calculated by the intake air amount calculating means.

  According to the eighth aspect of the present invention, if the air-fuel ratio detected by the exhaust gas sensor is on the fuel rich side even after a predetermined time has elapsed from the start of changing the fluctuation range or fluctuation period, the degree of deterioration of the catalyst is regarded as small. be able to. Therefore, the degree of deterioration of the catalyst can be determined without waiting for the air-fuel ratio to change from the fuel rich side to the fuel lean side.

  According to the ninth aspect of the present invention, if the air-fuel ratio detected by the exhaust gas sensor is on the fuel lean side even after a predetermined time has elapsed from the start of changing the fluctuation range or fluctuation period, the degree of deterioration of the catalyst is considered large. be able to. Therefore, the degree of deterioration of the catalyst can be determined without waiting until the air-fuel ratio changes from the fuel lean side to the fuel rich side.

  According to the tenth aspect of the invention, the target air-fuel ratio is changed around the fuel rich side value from the theoretical air-fuel ratio. Even with a normal catalyst, the reaction rate of the oxygen release reaction tends to be slightly lower than that of the oxygen storage reaction. For this reason, even in the case of a normal catalyst, the air-fuel ratio detected by the exhaust gas sensor after the start of fluctuation of the target air-fuel ratio may be on the fuel lean side. By setting the fluctuation center of the target air-fuel ratio to the fuel-rich side, the air-fuel ratio downstream of the catalyst can be reliably set to the fuel-rich side in the case of a normal catalyst. Therefore, the deterioration determination of the catalyst can be performed with higher accuracy.

  According to the eleventh aspect, the target air-fuel ratio is changed when the intake air amount of the internal combustion engine is equal to or smaller than a predetermined value. When the amount of intake air in the internal combustion engine is small, the amount of reducing gas flowing into the catalyst decreases as the amount of exhaust gas flowing into the catalyst decreases. As a result, an environment in which the oxygen releasing reaction hardly occurs in the catalyst can be obtained, and the deterioration of the catalyst can be accurately determined.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a schematic diagram showing the configuration of an internal combustion engine system according to Embodiment 1 of the present invention. Although the internal combustion engine system described in the first embodiment has a plurality of cylinders, only one of them is shown in FIG.
As shown in FIG. 1, the system according to the first embodiment includes a cylinder block 4 having a piston 2 therein. The cylinder block 4 is provided with a water temperature sensor 6. The water temperature sensor 6 is configured to detect the cooling water temperature.

  A cylinder head 8 is assembled to the upper part of the cylinder block 4. A space from the upper surface of the piston 2 to the cylinder head 8 forms a combustion chamber 10. The cylinder head 8 is provided with a spark plug 12 that ignites the air-fuel mixture in the combustion chamber 10.

  Further, the cylinder head 8 includes an intake port 14 that communicates with the combustion chamber 10. An intake valve 16 is provided at a connection portion between the intake port 14 and the combustion chamber 10. An intake passage 20 is connected to the intake port 14. In the vicinity of the intake port 14, an injector 18 for injecting fuel is provided in the vicinity. An air cleaner 22 is provided at the upstream end of the intake passage 20. An air flow meter 24 is provided downstream of the air cleaner 22 in the intake passage 20. The air flow meter 24 is configured to detect the intake air amount Ga. A throttle valve 26 is provided downstream of the air flow meter 24. A throttle sensor 27 is provided in the vicinity of the throttle valve 26. The throttle sensor 27 is configured to detect the throttle opening degree TA. A surge tank 28 is provided downstream of the throttle valve 26.

  The cylinder head 8 includes an exhaust port 30 that communicates with the combustion chamber 10. An exhaust valve 32 is provided at the connection between the exhaust port 30 and the combustion chamber 10. An exhaust passage 34 is connected to the exhaust port 30. A catalyst 38 is provided in the exhaust passage 34. The catalyst 38 is configured to purify exhaust gas discharged from the combustion chamber 10. An air-fuel ratio sensor 36 is provided upstream of the catalyst 38 in the exhaust passage 34. The air-fuel ratio sensor 36 is configured to detect the exhaust air-fuel ratio. An oxygen sensor 40 is provided downstream of the catalyst 38. The oxygen sensor 40 is configured to invert the output signal depending on whether the air-fuel ratio is rich or lean. The catalyst 38 is provided with a catalyst temperature sensor 42 that detects the temperature of the catalyst 38.

Further, the system of the first embodiment includes an ECU (Electronic Control Unit) 50 as a control device. A spark plug 12, an injector 18, a throttle valve 26, and the like are connected to the output side of the ECU 50. In addition to the water temperature sensor 6, the air flow meter 24, the throttle sensor 27, the air-fuel ratio sensor 36, the oxygen sensor 40, and the catalyst temperature sensor 42, a crank angle sensor 44 is connected to the input side of the ECU 50. The crank angle sensor 44 is configured to detect the rotation angle of the crankshaft 46. The ECU 50 performs overall control of the internal combustion engine such as fuel injection control and ignition timing control based on the output of each sensor.
Further, the ECU 50 determines based on the output of the water temperature sensor 6 whether or not the internal combustion engine has been warmed up. Further, the ECU 50 determines whether or not the warming-up of the catalyst 38 has been completed based on the output of the catalyst temperature sensor 42.
Further, the ECU 50 calculates the engine speed NE based on the output of the crank angle sensor 44.
Moreover, ECU50 determines whether it is a steady operation. Whether the operation is steady or not can be determined by parameters such as the intake air amount Ga, the engine speed NE, the throttle opening TA, the accelerator opening, and the like.
Further, as will be described later, the ECU 50 controls the target air-fuel ratio and determines the deterioration of the catalyst 38 based on the output of the oxygen sensor 40 (hereinafter referred to as “oxygen sensor output”) at that time.

[Features of Embodiment 1]
FIG. 2 is a conceptual diagram showing an oxygen storage reaction and an oxygen release reaction in a catalyst. As shown in FIG. 2, when a fuel-lean exhaust gas flows into the catalyst 38, excess oxygen in the exhaust gas is composed of a catalyst carrier (for example, a noble metal such as Pt, Pd, Rh, Ce) 38a. Is occluded by. On the other hand, when exhaust gas rich in fuel, that is, reducing gas (for example, CO, HC) flows into the catalyst 38, the reducing gas is oxidized by oxygen released from the catalyst carrier 38a and discharged as CO ₂ or H ₂ O. Is done.

  By the way, it is known that the reaction rate of the oxygen storage reaction is larger than the reaction rate of the oxygen releasing reaction in the catalyst. This tendency becomes more prominent as the degree of deterioration of the catalyst increases. That is, when the catalyst carrier 38a deteriorates due to sintering or the like, the reaction rate of the oxygen release reaction in the catalyst 38 is greatly reduced. For this reason, in the deteriorated catalyst (hereinafter referred to as “deteriorated catalyst”), the reaction rate of the oxygen release reaction becomes very small compared to the reaction rate of the oxygen storage reaction. Therefore, if the target air-fuel ratio is changed between the fuel rich side and the fuel lean side in a short cycle, it can be assumed that only the oxygen storage reaction proceeds in the deteriorated catalyst. Then, the amount of oxygen stored in the deteriorated catalyst eventually reaches a saturation amount, and fuel lean exhaust gas blows out from the deteriorated catalyst, so that the oxygen sensor output becomes a lean output.

The inventor investigated the oxygen sensor output after a predetermined time had elapsed since the target air-fuel ratio was changed. This investigation was performed for each fluctuation cycle by changing the fluctuation cycle of the target air-fuel ratio from a short cycle to a long cycle. This investigation was conducted for each of the large, medium, and small degree of deterioration catalysts. The survey results are shown in FIG. FIG. 3 is a diagram showing the relationship between the fluctuation cycle of the target air-fuel ratio and the oxygen sensor output after a predetermined time has elapsed since the start of fluctuation of the target air-fuel ratio. Here, the fluctuation center of the target air-fuel ratio was set to 14.55 on the weak fuel rich side, and the fluctuation width was ± 5% of the fluctuation center value.
As shown in FIG. 3, when the fluctuation cycle of the target air-fuel ratio is set to a long cycle, the difference between the oxygen sensor output when the catalyst deterioration is moderate and the oxygen sensor output when the catalyst deterioration is large. Is small. For this reason, it is difficult to detect a highly deteriorated catalyst with high accuracy. However, by setting the fluctuation cycle to a short cycle, the difference between the oxygen sensor output when the catalyst deterioration is moderate and the oxygen sensor output when the catalyst deterioration is large is increased. Therefore, it is possible to detect a highly deteriorated catalyst with high accuracy.

FIG. 4 is a diagram illustrating a catalyst deterioration determination method according to the first embodiment. Specifically, FIG. 4A is a diagram showing a change in the target air-fuel ratio, and FIG. 4B is a diagram showing a state of the oxygen sensor output after a predetermined time has elapsed from the start of the change in the target air-fuel ratio. .
As shown in FIG. 4A, the target air-fuel ratio is changed alternately between the fuel rich side and the fuel lean side. Here, the fluctuation cycle eabyfrefci of the target air-fuel ratio is a cycle that is sufficiently shorter than the cycle in which the oxygen storage capacity (OSC) of a normal catalyst (hereinafter referred to as “normal catalyst”) fails, for example, 0.5 Hz It is the above value. Further, the fluctuation center eabyfrefc is, for example, the value 14.55, and the fluctuation width eabyfrefd is, for example, a value not less than 0.1 and not more than 0.5.
As described above, when the target air-fuel ratio is changed in a short cycle, the air-fuel ratio of the exhaust gas flowing into the catalyst is changed accordingly. For this reason, oxygen storage reaction and oxygen release reaction occur alternately in the catalyst. As described above, in the case of a deteriorated catalyst, the reaction rate of the oxygen release reaction is very low compared to the oxygen storage reaction, so that only the oxygen storage reaction apparently proceeds. Therefore, in the case of a deteriorated catalyst, the amount of stored oxygen reaches the saturation amount earlier than that of the normal catalyst, and the air-fuel ratio of the exhaust gas flowing through the catalyst becomes the fuel lean side. Therefore, as shown in FIG. 4B, the oxygen sensor output after a predetermined time has elapsed from the start of the fluctuation of the target air-fuel ratio is a lean output for a deteriorated catalyst, but a rich output for a normal catalyst. is there.

  Therefore, according to the first embodiment, the target air-fuel ratio is changed between the fuel rich side and the fuel lean side in a short cycle, and the catalyst is deteriorated based on the oxygen sensor output after a predetermined time has elapsed from the start of the change. Can be determined. Therefore, since it is not necessary to calculate the oxygen storage capacity of the catalyst, it is possible to accurately determine the deterioration of the catalyst.

[Specific Processing in Embodiment 1]
FIG. 5 is a flowchart showing the catalyst deterioration determination control executed by the ECU 50 in the first embodiment.
According to the flow shown in FIG. 5, it is first determined whether or not the internal combustion engine and the catalyst 38 have been warmed up (step 100). If it is determined in step 100 that the warm-up has been completed, it is determined whether or not the catalyst deterioration determination control can be executed. Specifically, whether or not the target air-fuel ratio can be accurately controlled. It is determined whether or not (step 102). Whether the operation is steady or not can be determined based on the intake air amount Ga, the accelerator opening, and the like. If it is determined in step 100 that the warm-up has not been completed, and if it is determined in step 102 that the catalyst deterioration determination control cannot be executed, this control is terminated. In this case, it is determined that the deterioration determination control of the catalyst 38 cannot be performed with high accuracy.

If it is determined in step 102 that the catalyst deterioration determination control can be executed, the target air-fuel ratio starts to change (step 104). In step 104, the ECU 50 reads preset values of the fluctuation center eabyfrefc, fluctuation width eabyfrefd, and fluctuation period eabyfrefci in order to change the target air-fuel ratio alternately between the fuel rich side and the fuel lean side in a short cycle.
Here, the fluctuation center eabyfrefc is preferably set to a value on the fuel rich side that is weaker than the stoichiometric air-fuel ratio (for example, a value of 14.55). Even in the case of a normal catalyst, the oxygen sensor output may be a lean output because the reaction rate of the oxygen release reaction is slightly faster than the oxygen storage reaction. In this routine, when the oxygen sensor output is a lean output, it is determined that the catalyst is a deteriorated catalyst (step 108 described later). Therefore, by setting the fluctuation center eabyfrefc to a value on the weak fuel rich side, the oxygen sensor output can be made rich in the case of a normal catalyst, and the deterioration of the catalyst can be accurately determined. The fluctuation range eabyfrefd is preferably a value of 0.1 or more and 0.5 or less, for example. The fluctuation period eabyfrefci is a period that is sufficiently shorter than the period in which the oxygen storage capacity of the normal catalyst breaks down. For example, a value of 0.5 Hz or more is suitable.
When the target air-fuel ratio is changed in a short cycle in this way, the fuel-lean exhaust gas and the fuel-rich exhaust gas alternately flow into the catalyst in a short cycle, and the oxygen storage reaction and the oxygen release reaction alternate in a short cycle. Occur. However, in the deteriorated catalyst, the reaction rate of the oxygen releasing reaction is greatly reduced, so that only the oxygen storage reaction apparently proceeds. That is, in the deteriorated catalyst, oxygen continues to be occluded after the target air-fuel ratio starts to change.

  Next, it is determined whether or not the oxygen sensor output is changing in synchronization with the change in the target air-fuel ratio (step 105). In this step 105, it is determined whether or not the oxygen storage capacity of the catalyst 38 is close to zero, that is, whether or not the catalyst 38 is abnormally deteriorated. When it is determined that the oxygen sensor output is fluctuating, that is, when it is determined that the catalyst 38 is abnormally deteriorated, a check lamp provided in the vehicle is turned on (step 110) to determine deterioration. Control is terminated (step 112).

On the other hand, if it is determined in step 105 that the oxygen sensor output has not fluctuated, that is, if it is determined that the catalyst 38 has not deteriorated abnormally, it is sucked into the internal combustion engine after the start of fluctuation of the target air-fuel ratio. It is determined whether the air amount (hereinafter referred to as “integrated intake air amount”) egasam is larger than the set value egasam0. Here, the ECU 50 integrates the amount of air sucked into the internal combustion engine after the start of fluctuation of the target air-fuel ratio by a routine different from this routine. The ECU 50 reads the integrated air amount as the integrated intake air amount egasam. The set value egasam0 is a value set for each vehicle in consideration of the catalyst size and the like.
In this step 106, it is determined whether or not it is estimated that the influence of the change in the target air-fuel ratio is reflected in the catalyst 38 and the oxygen sensor output. More specifically, when oxygen has been occluded in the deteriorated catalyst since the start of the change in the target air-fuel ratio, exhaust gas sufficient for the amount of oxygen stored in the deteriorated catalyst to reach the saturation amount is discharged from the internal combustion engine. It is determined whether or not it is estimated that it has been performed.
When it is determined in step 106 that the integrated intake air amount egasam is equal to or less than the set value egasam0, that is, when it is estimated that the influence of the change in the target air-fuel ratio is not reflected in the catalyst 38 and the oxygen sensor output. The process of step 102 is executed again.
On the other hand, when it is determined in step 106 that the integrated intake air amount egasam is larger than the set value egasam0, that is, when it is estimated that the influence of the change in the target air-fuel ratio is reflected in the catalyst, It is determined whether or not the oxygen sensor output gaoxsav is smaller than the deterioration determination reference value gaoxsav0 (step 108). That is, in this step 108, it is determined whether or not the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side. Further, the deterioration determination reference value gaoxsav0 is a value set for each vehicle.

  If it is determined in step 108 that the average oxygen sensor output gaoxsav is smaller than the deterioration determination reference value gaoxsav0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side, It is determined that a saturated amount of oxygen is stored in the catalyst. That is, since the catalyst is deteriorated, only the oxygen storage reaction apparently proceeds in the catalyst, and it is determined that the oxygen storage amount has reached the saturation amount. In this case, the change in the target air-fuel ratio is stopped and a check lamp provided in the vehicle is turned on to notify the vehicle driver of catalyst deterioration (step 110), and the catalyst deterioration determination control is ended (step 112). .

  On the other hand, if it is determined in step 108 that the average oxygen sensor output gaoxsav is greater than or equal to the deterioration determination reference value gaoxsav0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is not on the fuel lean side, It is determined that the oxygen storage amount has not reached the saturation amount. That is, since the catalyst has not deteriorated, only the oxygen storage reaction apparently does not proceed in the catalyst, and it is determined that the oxygen storage capacity of the catalyst has not failed. In this case, the target air-fuel ratio fluctuation control is stopped without turning on the check lamp, and the catalyst deterioration determination control is terminated (step 112).

As described above, according to the routine shown in FIG. 5, the target air-fuel ratio is changed in a short cycle, and the time when the integrated intake air amount egasam after the start of the change reaches the predetermined amount egasam0 is detected. When the oxygen sensor output gaoxsav is on the fuel lean side, it can be determined that the catalyst has deteriorated. Therefore, it is possible to accurately determine the deterioration of the catalyst without being based on the oxygen storage capacity of the catalyst. That is, the deterioration catalyst can be detected without calculating the oxygen storage capacity.
Furthermore, according to this routine, the oxygen sensor output in the case of a normal catalyst can be made rich by setting the fluctuation center of the target air-fuel ratio to the fuel rich side from the theoretical air-fuel ratio. Therefore, when the oxygen sensor output is a lean output, it can be reliably determined that the catalyst has deteriorated. Accordingly, erroneous determination can be prevented, and catalyst deterioration determination can be performed with high accuracy.

  By the way, in the first embodiment, it is assumed that the warm-up is completed (step 100) and that the operation is steady (step 102) when starting the fluctuation of the target air-fuel ratio. You may add to the conditions that quantity is below a predetermined value. When the amount of intake air is small (for example, 10 g / sec or less), the amount of exhaust gas flowing into the catalyst 38 decreases and the amount of reducing gas flowing into the catalyst 38 also decreases. Therefore, since the catalyst deterioration determination control can be executed under the condition that the oxygen releasing reaction is less in the catalyst, the catalyst deterioration determination can be performed with higher accuracy. (The same applies to other embodiments described later.)

  In the first embodiment, the air-fuel ratio downstream of the catalyst is detected by the oxygen sensor 40, but a system in which the air-fuel ratio downstream of the catalyst is detected by the air-fuel ratio sensor can be used. Also in this case, the same effect as in the first embodiment can be obtained. (The same applies to other embodiments described later.)

  In the first embodiment, the specific value of the fluctuation range eabyfrefd of the target air-fuel ratio is set to a value not less than 0.1 and not more than 0.5. However, the value is not limited to this value and can be changed without departing from the essence of the present invention. May be. It can be set appropriately for each vehicle according to the catalyst size and the like.

  In the first embodiment, a specific value of the target air-fuel ratio fluctuation period eabyfrefci is 0.5 Hz or more. However, the value is not limited to this value and may be changed without departing from the essence of the present invention. Also good. The fluctuation cycle is such that the reaction rate difference between the oxygen storage reaction and the oxygen release reaction is greater than or equal to a predetermined value in a deteriorated catalyst (a catalyst having a high degree of deterioration), that is, it can be assumed that only the oxygen storage reaction proceeds in the deteriorated catalyst. Any numerical value can be used. By setting it as such a state, a catalyst with a moderate deterioration degree and a catalyst with a large deterioration degree can be distinguished with sufficient accuracy. By setting the fluctuation cycle to a cycle shorter than at least the cycle in which the oxygen storage capacity of the normal catalyst fails, the above-described state can be obtained.

  In the first embodiment, the ECU 50 executes the process of step 104, so that the “air-fuel ratio control means” in the first invention executes the process of step 108, and “ "Catalyst degradation determination means" is realized respectively.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. The system of the second embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 7 to be described later using the hardware configuration shown in FIG.

[Features of Embodiment 2]
FIG. 6 is a diagram illustrating a catalyst deterioration determination method according to the second embodiment. Specifically, FIG. 6A is a diagram showing a change in the target air-fuel ratio, and FIG. 6B is a diagram showing a change in the oxygen sensor output accompanying the change in the target air-fuel ratio.
First, as in the first embodiment, the target air-fuel ratio is changed in a cycle sufficiently shorter than the cycle in which the oxygen storage capacity of the normal catalyst fails. In the second embodiment, after a certain time has elapsed from the start of the fluctuation, as shown in FIG. 6A, the fluctuation range of the target air-fuel ratio is gradually reduced. Here, the smaller the fluctuation range of the target air-fuel ratio is, the lower the concentration of the reducing gas flowing into the catalyst 38 becomes, so that an environment in which oxygen is hardly released from the catalyst 38 is obtained. By setting such an environment, not only the deteriorated catalyst but also the normal catalyst eventually loses its oxygen storage capacity, and the air-fuel ratio of the exhaust gas flowing through the catalyst becomes the fuel lean side. However, as described above, the deterioration rate of the oxygen release reaction is greater in the deteriorated catalyst than in the normal catalyst, that is, the reaction rate difference between the oxygen storage reaction and the oxygen release reaction is greater in the deteriorated catalyst. For this reason, the oxygen storage capacity breaks down earlier in the deteriorated catalyst than in the normal catalyst. As a result, as shown in FIG. 6B, the time t1 when the oxygen sensor output in the case of the deteriorated catalyst is reversed from the rich output to the lean output is earlier than the time t2 in the case of the normal catalyst. Further, the inversion time of the oxygen sensor output is earlier when the degree of deterioration is larger than when the degree of deterioration of the catalyst is small.

  Therefore, according to the second embodiment, the variation degree of the target air-fuel ratio is gradually reduced, and the deterioration of the catalyst is accurately determined by detecting the time point when the oxygen sensor output is reversed from the rich output to the lean output. be able to. Furthermore, it is possible to accurately detect the degree of deterioration of the catalyst based on the inversion time of the oxygen sensor output.

[Specific Processing in Second Embodiment]
FIG. 7 is a flowchart showing the catalyst deterioration determination control executed by the ECU 50 in the second embodiment.
According to the flow shown in FIG. 7, first, similarly to the first embodiment, when it is determined in step 100 that the warm-up is completed and it is determined in step 102 that the catalyst deterioration determination control can be executed. First, a change in the target air-fuel ratio is started (step 104).

Next, similarly to step 105 of the flow shown in FIG. 5, it is determined whether or not the oxygen sensor output is changing in synchronization with the change of the target air-fuel ratio (step 114). If it is determined in step 114 that the oxygen sensor output is fluctuating, that is, if it is determined that the catalyst 38 is abnormally deteriorated, a check lamp provided in the vehicle is turned on (step 136). ), And the deterioration determination control is terminated (step 138).
On the other hand, if it is determined in step 114 that the oxygen sensor output has not fluctuated, that is, if it is determined that the catalyst 38 has not abnormally deteriorated, the integrated intake air amount egasam after the start of fluctuation of the target air-fuel ratio is determined. Is greater than the set value egasam1 (step 116). As in the first embodiment, the ECU 50 reads the air amount integrated in another routine as the integrated intake air amount egasam. In this step 116, it is determined whether or not a certain amount of exhaust gas has flowed into the catalyst in order to stabilize the state of the catalyst. Therefore, this set value egasam1 is a value smaller than the set value egasam0 used in step 106 of the flow shown in FIG. The set value egasam1 is a value set for each vehicle in consideration of the catalyst size and the like.
If it is determined in step 116 that the integrated intake air amount egasam is equal to or less than the set value egasam1, that is, if it is determined that a certain amount of exhaust gas does not flow into the catalyst 38, the process of step 102 is performed again. Execute.

  If it is determined in step 116 that the integrated intake air amount egasam is larger than the set value egasam1, and if it is determined that a certain amount of exhaust gas has flowed into the catalyst, the intake air is the same as in step 102. It is determined whether or not the catalyst deterioration determination control can be continued based on the amount Ga, the accelerator opening, etc. (step 118). If it is determined in step 118 that the catalyst deterioration determination control cannot be continued, this control is terminated.

  If it is determined in step 118 that the catalyst deterioration determination control can be continued, it is determined whether or not the oxygen sensor output gaoxs is larger than the reference value gaoxs0 (step 120). In this step 120, it is determined whether or not the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side. If it is determined in step 120 that the oxygen sensor output gaoxs is less than or equal to the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side, It is judged that the occlusion ability has failed early. Also in this case, since it is determined that the catalyst is largely deteriorated, a check lamp provided in the vehicle is turned on (step 136).

  If it is determined in step 120 that the oxygen sensor output gaoxs is greater than the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side, the target air-fuel ratio is determined. Attenuation of the fluctuation range eabyfrefd is started (step 122). In step 122, the ECU 50 reads the value of the attenuation speed eabyfrefgd having a preset fluctuation range. By attenuating the fluctuation range of the target air-fuel ratio, the concentration of the reducing gas flowing into the catalyst 38 is lowered, so that an environment in which the oxygen release reaction hardly occurs in the catalyst 38 is created.

  Next, in the same manner as in step 114, it is determined whether or not the oxygen sensor output is changing in synchronization with the change in the target air-fuel ratio (step 124). If it is determined in step 124 that the oxygen sensor output is fluctuating, that is, if it is determined that the catalyst is abnormally deteriorated, a check lamp provided in the vehicle is turned on (step 136).

  On the other hand, if it is determined in step 124 that the oxygen sensor output has not fluctuated, that is, if it is determined that the catalyst has not deteriorated abnormally, whether or not the oxygen sensor output gaoxs is smaller than the reference value gaoxs0. Is determined (step 126). In step 126, it is determined whether or not the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side. If it is determined in step 126 that the oxygen sensor output gaoxs is greater than or equal to the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is not on the fuel lean side but on the fuel rich side. Then, it is determined whether or not the integrated intake air amount egasam after the start of fluctuation of the target air-fuel ratio is larger than the set value egasam0 (step 128). The ECU 50 reads the air amount integrated in another routine as the integrated intake air amount egasam. In this step 128, it is determined whether or not the fluctuation range of the target air-fuel ratio is sufficiently small until it can be determined that the catalyst is a normal catalyst. The set value egasam0 is a value set for each vehicle in consideration of the catalyst size and the like.

  If it is determined in step 128 that the integrated intake air amount egasam is equal to or less than the set value egasam0, that is, if it is determined that the fluctuation range of the target air-fuel ratio is not sufficiently small, the process of step 118 is executed again. To do. On the other hand, if it is determined in step 128 that the integrated intake air amount egasam is larger than the set value egasam0, it is determined that the fluctuation range of the target air-fuel ratio is sufficiently small. That is, although the fluctuation range of the target air-fuel ratio is sufficiently small, it is determined that the degree of deterioration of the catalyst is small because the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side. In this case, the deterioration determination is performed without waiting until the oxygen sensor output gaoxs becomes smaller than the set value gaoxs0, that is, without waiting until the air-fuel ratio of the exhaust gas flowing through the catalyst 38 changes from the fuel rich side to the fuel lean side. Control is terminated (step 138).

If it is determined in step 126 that the oxygen sensor output gaoxs is smaller than the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side, the target air-fuel ratio is determined. The integrated intake air amount egasum1 is calculated from the start of the attenuation of the fluctuation range until the oxygen sensor output gaoxs is determined to be smaller than the reference value gaoxs0 (step 130). Here, the ECU 50 can read the air amount integrated in another routine as the integrated intake air amount egasum1.
Next, the deterioration degree of the catalyst corresponding to the calculated integrated intake air amount egasum1 is calculated with reference to a map stored in advance in the ECU 50 (step 132). In this map, the catalyst deterioration degree is set to be larger as the integrated intake air amount egasum1 is smaller. Thereby, the deterioration degree of the catalyst can be accurately obtained based on the integrated intake air amount egasum1.

Further, it is determined whether or not the integrated intake air amount egasum1 is smaller than the catalyst deterioration determination reference value egasumn (step 134). The catalyst deterioration criterion value egasumn is a value set for each vehicle in consideration of the catalyst size and the like. If it is determined in step 134 that the integrated intake air amount egasum1 is smaller than the catalyst deterioration determination reference value egasumn, it is determined that the catalyst is largely deteriorated. In this case, a check lamp provided in the vehicle is turned on (step 136), and then the catalyst deterioration determination control is ended (step 138).
On the other hand, if it is determined in step 134 that the integrated intake air amount egasum1 is equal to or greater than the catalyst deterioration determination reference value egasumn, it is determined that the catalyst deterioration is within an allowable range. In this case, the catalyst deterioration determination control is stopped without turning on the check lamp (step 138).

  As described above, according to the routine shown in FIG. 7, the fluctuation range eabyfrefd of the target air-fuel ratio is gradually attenuated, and the integrated intake air amount egasum1 from the start of attenuation until the oxygen sensor output goxs is inverted is calculated. Based on the calculated integrated intake air amount egasum1, the deterioration of the catalyst can be determined. Therefore, it is possible to accurately determine the deterioration of the catalyst without being based on the oxygen storage capacity of the catalyst. Furthermore, it is possible to accurately detect a catalyst having a high degree of deterioration.

  In the second embodiment, the ECU 50 executes the processing of steps 104 and 122, so that the “air-fuel ratio control means” in the second invention executes the processing of step 130, and the second invention. The “intake air amount calculation means” in FIG. 6 implements the “catalyst deterioration determination means” in the second invention by executing the processing of step 134. Further, the “catalyst deterioration determining means” according to the sixth aspect of the present invention is realized by the ECU 50 executing the process of step 132.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIGS. The system of the third embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 8 to be described later using the hardware configuration shown in FIG.

[Features of Embodiment 3]
FIG. 8 is a diagram illustrating a catalyst deterioration determination method according to the third embodiment. Specifically, FIG. 8A is a diagram showing a change in the target air-fuel ratio, and FIG. 8B is a diagram showing a change in the oxygen sensor output accompanying the change in the target air-fuel ratio.
In the second embodiment, by gradually reducing the fluctuation range of the target air-fuel ratio, an environment in which oxygen is hardly released from the catalyst gradually is set, and the time point when the oxygen sensor output is reversed from the rich output to the lean output is detected.

  In the third embodiment, first, the target air-fuel ratio has a cycle that is sufficiently shorter than the cycle in which the oxygen storage capacity of the normal catalyst fails and that has a fluctuation range smaller than the fluctuation range of the target air-fuel ratio in the first embodiment. Fluctuate. As described above, the smaller the fluctuation range of the target air-fuel ratio, the lower the concentration of the reducing gas flowing into the catalyst, so that an environment in which oxygen is hardly released from the catalyst is created. For this reason, in the case of a normal catalyst as well as a deteriorated catalyst, the oxygen storage capacity breaks down, and the oxygen sensor output becomes a lean output. Thus, after the oxygen sensor output has changed from the rich output to the lean output, that is, after a certain time has elapsed from the start of the target air-fuel ratio change, as shown in FIG. Enlarge. By gradually increasing the fluctuation range in this way, an environment in which oxygen is easily released from the catalyst is created. Therefore, the reaction rate of the oxygen releasing reaction in the catalyst is gradually increased. The reaction rate of the oxygen release reaction is lower with the deteriorated catalyst than the normal catalyst, that is, the reaction rate difference between the oxygen storage reaction and the oxygen release reaction is smaller with the normal catalyst than with the deteriorated catalyst. For this reason, the failure of the oxygen storage capacity is resolved earlier in the normal catalyst than in the deteriorated catalyst. As a result, as shown in FIG. 8B, the time t3 when the oxygen sensor output for the normal catalyst is reversed from the lean output to the rich output is earlier than the time t4 for the deteriorated catalyst. Further, the reversal time of the oxygen sensor output is earlier when the degree of deterioration is smaller than when the degree of deterioration of the catalyst is large.

  Therefore, according to the third embodiment, the fluctuation range of the target air-fuel ratio is gradually increased, and the deterioration of the catalyst is accurately determined by detecting the time point when the oxygen sensor output changes from the lean output to the rich output. be able to. Furthermore, it is possible to accurately detect the degree of deterioration of the catalyst based on the inversion time of the oxygen sensor output.

[Specific Processing in Embodiment 3]
FIG. 9 is a flowchart showing catalyst deterioration determination control executed by the ECU 50 in the third embodiment.
According to the flow shown in FIG. 9, first, as in the first embodiment, when it is determined in step 100 that the warm-up has been completed, and in step 102, it is determined that the catalyst deterioration determination control can be executed. First, a change in the target air-fuel ratio is started (step 104). Here, the fluctuation range eabyfrefd read by the ECU 50 is a value smaller than the fluctuation range read in step 104 of the flow of FIG. Thereby, the target air-fuel ratio is controlled with a cycle sufficiently shorter than the cycle in which the oxygen storage capacity of the normal catalyst fails and with a fluctuation range smaller than the fluctuation range in the first embodiment.

  Next, as in the second embodiment, it is determined whether or not the oxygen sensor output is fluctuating in synchronization with the fluctuation of the target air-fuel ratio (step 114). If it is determined in step 114 that the oxygen sensor output is fluctuating, that is, if it is determined that the catalyst is abnormally deteriorated, a check lamp provided in the vehicle is turned on (step 136). ), And the deterioration determination control is terminated (step 138).

  On the other hand, if it is determined in step 114 that the oxygen sensor output has not fluctuated, that is, if it is determined that the catalyst has not abnormally deteriorated, the accumulated intake air amount egasam after the start of fluctuation of the target air-fuel ratio is calculated. It is determined whether or not it is larger than the set value egasam1 (step 116). The ECU 50 reads the air amount integrated in another routine as the integrated intake air amount egasam. If it is determined in step 116 that the integrated intake air amount egasam is less than or equal to the set value egasam1, that is, it is determined that a certain amount of exhaust gas necessary to stabilize the state of the catalyst does not flow into the catalyst. In that case, the process of step 102 is executed again.

  If it is determined in step 116 that the integrated intake air amount egasam is greater than the set value egasam1, that is, if it is determined that a certain amount of exhaust gas has flowed into the catalyst, the catalyst deterioration determination control can be continued. It is determined whether or not there is (step 118). If it is determined in step 118 that the catalyst deterioration determination control cannot be continued, this control is terminated.

If it is determined in step 118 that the catalyst deterioration determination control can be continued, it is determined whether or not the oxygen sensor output gaoxs is smaller than the reference value gaoxs0 (step 121). In this step 121, it is determined whether or not the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side. Here, since the fluctuation range is set to be small in step 104, an environment in which the oxygen release reaction hardly occurs in the catalyst is created. Therefore, normally, not only a deteriorated catalyst but also a normal catalyst, the reaction rate of the oxygen release reaction in the catalyst is greatly reduced, so the air-fuel ratio of the exhaust gas flowing through the catalyst is on the fuel lean side, and the oxygen sensor output gaoxs is smaller than the reference value gaoxs0.
If it is determined in step 121 that the oxygen sensor output gaoxs is greater than or equal to the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side, the air-fuel ratio In order to change the fuel rich side to the fuel lean side, the process of step 102 is executed again.

  If it is determined in step 121 that the oxygen sensor output gaoxs is smaller than the deterioration determination reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side, the target Amplification of the air-fuel ratio fluctuation range eabyfrefd is started (step 140). In step 140, the ECU 50 reads the value of the amplification rate eabyfrefgu having a preset fluctuation range. By amplifying the fluctuation range of the target air-fuel ratio, the concentration of the reducing gas flowing into the catalyst 38 increases, so that an environment in which oxygen release reaction is likely to occur in the catalyst 38 is obtained.

  Next, in the same manner as in step 114, it is determined whether or not the oxygen sensor output is changing in synchronization with the change in the target air-fuel ratio (step 124). If it is determined in step 124 that the oxygen sensor output is fluctuating, that is, if it is determined that the catalyst is abnormally deteriorated, a check lamp provided in the vehicle is turned on (step 136).

  On the other hand, if it is determined in step 124 that the oxygen sensor output has not fluctuated, that is, if it is determined that the catalyst has not deteriorated abnormally, whether or not the oxygen sensor output gaoxs is greater than the reference value gaoxs0. Is discriminated (step 142). In step 142, it is determined whether or not the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side. If it is determined in step 142 that the oxygen sensor output gaoxs is less than or equal to the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is not the fuel rich side but the fuel lean side. Then, it is determined whether or not the integrated intake air amount egasam after the start of fluctuation of the target air-fuel ratio is larger than the set value egasam0 (step 128). In this step 128, it is determined whether or not the fluctuation range of the target air-fuel ratio is sufficiently large until it can be determined that the catalyst has deteriorated.

If it is determined in step 128 that the integrated intake air amount egasam is equal to or less than the set value egasam0, that is, if it is determined that the fluctuation range of the target air-fuel ratio is not sufficiently large, the process of step 118 is executed again. To do.
On the other hand, if it is determined in step 128 that the integrated intake air amount egasam is larger than the set value egasam0, it is determined that the fluctuation range of the target air-fuel ratio is sufficiently large. That is, although the fluctuation range of the target air-fuel ratio is sufficiently large, it is determined that the degree of deterioration of the catalyst is large because the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side. In this case, the check provided in the vehicle is not waited until the oxygen sensor output gaoxs becomes larger than the set value gaoxs0, that is, without waiting until the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is reversed to the fuel rich side. The lamp is turned on (step 136), and the deterioration determination control is ended (step 138).

If it is determined in step 142 that the oxygen sensor output gaoxs is larger than the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side, the target air-fuel ratio is determined. The integrated intake air amount egasum2 is calculated from the start of amplification of the fluctuation range until the oxygen sensor output gaoxs is determined to be larger than the reference value gaoxs0 (step 144). The ECU 50 can read the air amount integrated in another routine as the integrated intake air amount egasum2.
Next, referring to a map stored in advance in the ECU 50, the degree of deterioration of the catalyst corresponding to the integrated intake air amount egasum2 is calculated (step 146). In the map, the degree of catalyst deterioration is set to increase as the integrated intake air amount egasum2 increases. Thereby, the deterioration degree of the catalyst can be accurately obtained based on the integrated intake air amount egasum2.

Further, it is determined whether or not the integrated intake air amount egasum2 is larger than the catalyst deterioration determination reference value egasumn (step 148). If it is determined in step 148 that the integrated intake air amount egasum2 is larger than the catalyst deterioration determination reference value egasumn, it is determined that the catalyst is largely deteriorated. In this case, a check lamp provided in the vehicle is turned on (step 136), and then the catalyst deterioration determination control is ended (step 138).
On the other hand, if it is determined in step 148 that the integrated intake air amount egasum2 is equal to or less than the catalyst deterioration determination reference value egasumn, it is determined that the catalyst deterioration is within an allowable range. In this case, the catalyst deterioration determination control is stopped without turning on the check lamp (step 138).

  As described above, according to the routine shown in FIG. 9, the fluctuation range eabyfrefd of the target air-fuel ratio is gradually amplified, and the integrated intake air amount egasum2 from the start of amplification to the inversion of the oxygen sensor output is calculated. The deterioration of the catalyst can be determined based on the integrated intake air amount. Therefore, it is possible to accurately determine the deterioration of the catalyst 38 without being based on the oxygen storage capacity of the catalyst. Furthermore, it is possible to accurately detect a catalyst having a high degree of deterioration.

  In the third embodiment, when the ECU 50 executes the processing of steps 104 and 140, the “air-fuel ratio control means” according to the third invention executes the processing of step 144, thereby executing the third invention. The “intake air amount calculation means” in FIG. 6 implements the “catalyst deterioration determination means” in the third invention by executing the processing of step 148. Further, the “catalyst deterioration determination means” according to the seventh aspect of the present invention is realized by the ECU 50 executing the process of step 132.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIGS. The system of the fourth embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 11 to be described later using the hardware configuration shown in FIG.

[Features of Embodiment 4]
FIG. 10 is a diagram illustrating a catalyst deterioration determination method according to the fourth embodiment. Specifically, FIG. 10A is a diagram showing a change in the target air-fuel ratio, and FIG. 10B is a diagram showing a change in the oxygen sensor output accompanying a change in the target air-fuel ratio.
In the fourth embodiment, first, the target air-fuel ratio is changed in a cycle that is sufficiently shorter than the cycle in which the oxygen storage capacity of the normal catalyst fails and that is longer than the fluctuation cycle in the first embodiment. As the target air-fuel ratio fluctuation period is longer, the amount of reducing gas flowing into the catalyst is increased, so that an environment in which oxygen is easily released from the catalyst is obtained. Then, after a lapse of a certain time from the start of the fluctuation, the fluctuation cycle of the target air-fuel ratio is gradually shortened as shown in FIG. By gradually shortening the fluctuation period in this way, the amount of reducing gas flowing into the catalyst is reduced, so that an environment in which oxygen is less likely to be released from the catalyst is created. By setting such an environment, not only the deteriorated catalyst but also the normal catalyst eventually loses its oxygen storage capacity, and the air-fuel ratio of the exhaust gas flowing through the catalyst becomes the fuel lean side. However, as described above, the deterioration rate of the oxygen release reaction is larger in the deteriorated catalyst than in the normal catalyst. large. For this reason, the oxygen storage capacity breaks down earlier in the deteriorated catalyst than in the normal catalyst. As a result, as shown in FIG. 10B, the time t5 when the oxygen sensor output in the case of the deteriorated catalyst is reversed from the rich output to the lean output is earlier than the time t6 in the case of the normal catalyst. Further, the inversion time of the oxygen sensor output is earlier when the degree of deterioration of the catalyst is larger than when the degree of deterioration of the catalyst is small.

  Therefore, according to the fourth embodiment, the deterioration period of the catalyst is accurately determined by gradually shortening the fluctuation cycle of the target air-fuel ratio and detecting the time point when the oxygen sensor output is reversed from the rich output to the lean output. be able to. Furthermore, it is possible to accurately detect the degree of deterioration of the catalyst based on the inversion time of the oxygen sensor output.

[Specific Processing in Embodiment 4]
FIG. 11 is a flowchart showing the catalyst deterioration determination control executed by the ECU 50 in the fourth embodiment.
According to the flow shown in FIG. 11, first, as in the first embodiment, it is determined that the warm-up has been completed in step 100, and it is determined in step 102 that the catalyst deterioration determination control can be executed. First, a change in the target air-fuel ratio is started (step 104). Here, the fluctuation cycle eabyfrefci read by the ECU 50 is a value longer than the fluctuation cycle read in step 104 of the flow of FIG. As a result, the target air-fuel ratio is controlled in a fluctuation cycle that is sufficiently shorter than the cycle in which the oxygen storage capacity of the normal catalyst fails and that is longer than the fluctuation cycle in the first embodiment.

  Next, as in the second embodiment, it is determined whether or not the oxygen sensor output is fluctuating in synchronization with the fluctuation of the target air-fuel ratio (step 114). If it is determined in step 114 that the oxygen sensor output is fluctuating, that is, if it is determined that the catalyst 38 is abnormally deteriorated, a check lamp provided in the vehicle is turned on (step 136) and the deterioration determination control is terminated (step 138).

  On the other hand, if it is determined in step 114 that the oxygen sensor output has not fluctuated, that is, if it is determined that the catalyst 38 has not abnormally deteriorated, the integrated intake air amount egasam after the start of fluctuation of the target air-fuel ratio is determined. Is greater than the set value egasam1 (step 116). The ECU 50 reads the air amount integrated in another routine as the integrated intake air amount egasam. If it is determined in step 116 that the integrated intake air amount egasam is less than or equal to the set value egasam1, that is, it is determined that a certain amount of exhaust gas necessary to stabilize the state of the catalyst does not flow into the catalyst. In that case, the process of step 102 is executed again.

  If it is determined in step 116 that the integrated intake air amount egasam is greater than the set value egasam1, that is, if it is determined that a certain amount of exhaust gas has flowed into the catalyst, the catalyst deterioration determination control can be continued. It is determined whether or not there is (step 118). If it is determined in step 118 that the catalyst deterioration determination control cannot be continued, this control is terminated.

  If it is determined in step 118 that the catalyst deterioration determination control can be continued, it is determined whether or not the oxygen sensor output gaoxs is larger than the reference value gaoxs0 (step 120). In this step 120, it is determined whether or not the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side. If it is determined in step 120 that the oxygen sensor output gaoxs is less than or equal to the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side, It is judged that the occlusion ability collapsed early. Also in this case, since it is determined that the catalyst is largely deteriorated, a check lamp provided in the vehicle is turned on (step 136).

  If it is determined in step 120 that the oxygen sensor output gaoxs is greater than the deterioration determination reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side, the target Attenuation of the air-fuel ratio fluctuation period eabyfrefci is started (step 150). In step 150, the ECU 50 reads the value of the attenuation rate eabyfrefcd having a preset fluctuation period. By attenuating the fluctuation cycle of the target air-fuel ratio, the amount of reducing gas flowing into the catalyst 38 is reduced, so that an environment in which the oxygen release reaction hardly occurs in the catalyst 38 is obtained.

  Next, in the same manner as in step 114, it is determined whether or not the oxygen sensor output is changing in synchronization with the change in the target air-fuel ratio (step 124). If it is determined in step 124 that the oxygen sensor output is fluctuating, that is, if it is determined that the catalyst is abnormally deteriorated, a check lamp provided in the vehicle is turned on (step 136).

  On the other hand, if it is determined in step 124 that the oxygen sensor output has not fluctuated, that is, if it is determined that the catalyst has not deteriorated abnormally, the oxygen after the start of attenuation of the fluctuation cycle of the target air-fuel ratio has started. It is determined whether or not the sensor output gaoxs is smaller than the reference value gaoxs0 (step 152). In step 152, it is determined whether or not the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side. If it is determined in step 152 that the oxygen sensor output gaoxs is greater than or equal to the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is not on the fuel lean side but on the fuel rich side. Then, it is determined whether or not the integrated intake air amount egasam after the start of fluctuation of the target air-fuel ratio is larger than the set value egasam0 (step 128). The ECU 50 reads the air amount integrated in another routine as the integrated intake air amount egasam. In step 128, it is determined whether or not the target air-fuel ratio fluctuation period is sufficiently short until it can be determined that the catalyst is a normal catalyst.

If it is determined in step 128 that the integrated intake air amount egasam is equal to or less than the set value egasam0, that is, if it is determined that the fluctuation cycle of the target air-fuel ratio is not sufficiently short, the process of step 118 is executed again. To do.
On the other hand, when it is determined in step 128 that the integrated intake air amount egasam is larger than the set value egasam0, it is determined that the fluctuation cycle of the target air-fuel ratio is sufficiently short. That is, it is determined that the degree of deterioration of the catalyst is small because the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel-rich side even though the fluctuation cycle of the target air-fuel ratio is sufficiently short. In this case, deterioration determination is not performed without waiting until the oxygen sensor output gaoxs becomes smaller than the set value gaoxs0, that is, without waiting until the air-fuel ratio of the exhaust gas flowing through the catalyst 38 changes from the fuel rich side to the fuel lean side. Control is terminated (step 138).

  If it is determined in step 152 that the oxygen sensor output gaoxs is smaller than the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side, the target air-fuel ratio The integrated intake air amount egasum3 from the start of the attenuation of the fluctuation period until the oxygen sensor output gaoxs is determined to be smaller than the reference value gaoxs0 is calculated (step 154). The ECU 50 can read the air amount integrated in another routine as the integrated intake air amount egasum3.

Next, referring to a map stored in advance in the ECU 50, the degree of catalyst deterioration corresponding to the integrated intake air amount egasum3 is calculated (step 156). In the map, the catalyst deterioration degree is set to be larger as the integrated intake air amount egasum3 is smaller. Thereby, the deterioration degree of the catalyst can be accurately obtained based on the integrated intake air amount egasum3.
Further, it is determined whether or not the integrated intake air amount egasum3 is smaller than the catalyst deterioration determination reference value egasumn (step 158). If it is determined in step 158 that the integrated intake air amount egasum3 is smaller than the catalyst deterioration determination reference value egasumn, it is determined that the catalyst has deteriorated. In this case, a check lamp provided in the vehicle is turned on (step 136), and then the catalyst deterioration determination control is ended (step 138).
On the other hand, if it is determined in step 158 that the integrated intake air amount egasum3 is equal to or greater than the catalyst deterioration determination reference value egasumn, it is determined that the catalyst deterioration is within an allowable range. In this case, the catalyst deterioration determination control is stopped without turning on the check lamp (step 138).

  As described above, according to the routine shown in FIG. 11, the fluctuation period eabyfrefci of the target air-fuel ratio is gradually attenuated, and the integrated intake air amount egasum3 from the start of attenuation until the oxygen sensor output gaoxs is inverted is calculated. Based on the calculated integrated intake air amount egasum3, it is possible to determine the deterioration of the catalyst. Therefore, it is possible to accurately determine the deterioration of the catalyst 38 without being based on the oxygen storage capacity of the catalyst. Furthermore, it is possible to accurately detect a catalyst having a high degree of deterioration.

  In the fourth embodiment, when the ECU 50 executes the processing of steps 104 and 150, the “air-fuel ratio control means” in the fourth invention executes the processing of step 154, so that the fourth invention is executed. The “intake air amount calculation means” in FIG. 4 implements the “catalyst deterioration determination means” in the fourth invention by executing the processing of step 158. Further, the “catalyst deterioration determining means” according to the sixth aspect of the present invention is realized by the ECU 50 executing the process of step 156.

Embodiment 5 FIG.
Next, Embodiment 5 of the present invention will be described with reference to FIG. 12 and FIG. The system of the fifth embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 13 to be described later using the hardware configuration shown in FIG.

[Features of Embodiment 5]
FIG. 12 is a diagram illustrating a catalyst deterioration determination method according to the fifth embodiment. Specifically, FIG. 12A is a diagram showing a change in the target air-fuel ratio, and FIG. 12B is a diagram showing a change in the oxygen sensor output accompanying the change in the target air-fuel ratio.
In the fourth embodiment, the target air-fuel ratio fluctuation period is gradually shortened to make it difficult for oxygen to be gradually released from the catalyst, and the time point at which the oxygen sensor output is reversed from the rich output to the lean output is detected.

  In the fifth embodiment, first, the target air-fuel ratio is changed in a cycle sufficiently shorter than the cycle in which the oxygen storage capacity of the normal catalyst fails. Here, it is preferable that the fluctuation cycle is shorter than that of the first embodiment. As described above, the shorter the target air-fuel ratio fluctuation period, the smaller the amount of reducing gas that flows into the catalyst, so that it becomes difficult for oxygen to be released from the catalyst. For this reason, in the case of a normal catalyst as well as a deteriorated catalyst, the oxygen storage capacity breaks down, and the oxygen sensor output becomes a lean output. Thus, after the oxygen sensor output becomes a lean output, that is, after a predetermined time has elapsed from the start of the change in the target air-fuel ratio, the change cycle of the target air-fuel ratio is gradually lengthened as shown in FIG. By gradually increasing the fluctuation period in this way, an environment in which oxygen is easily released from the catalyst is created. Therefore, the reaction rate of the oxygen releasing reaction in the catalyst is gradually increased. However, the reaction rate of the oxygen release reaction is lower in the deteriorated catalyst than in the normal catalyst, that is, the reaction rate difference between the oxygen storage reaction and the oxygen release reaction is larger in the catalyst than in the normal catalyst. For this reason, the failure of the oxygen storage capacity is resolved earlier in the normal catalyst than in the deteriorated catalyst. As a result, as shown in FIG. 12B, the time t7 when the oxygen sensor output for the normal catalyst is reversed from the lean output to the rich output is earlier than the time t8 for the deteriorated catalyst. Further, the reversal time of the oxygen sensor output is earlier when the degree of deterioration is smaller than when the degree of deterioration of the catalyst is large.

  Therefore, according to the fifth embodiment, the deterioration period of the catalyst is accurately determined by gradually increasing the fluctuation cycle of the target air-fuel ratio and detecting when the oxygen sensor output changes from lean output to rich output. be able to. Furthermore, it is possible to accurately detect the degree of deterioration of the catalyst based on the inversion time of the oxygen sensor output. Furthermore, it is possible to accurately detect a catalyst having a high degree of deterioration.

[Specific Processing in Embodiment 5]
FIG. 13 is a flowchart showing the catalyst deterioration determination control executed by the ECU 50 in the fifth embodiment.
According to the flow shown in FIG. 13, first, similarly to the first embodiment, when it is determined in step 100 that the warm-up has been completed, and in step 102, it is determined that the catalyst deterioration determination control can be executed. First, a change in the target air-fuel ratio is started (step 104). Here, the fluctuation cycle eabyfrefci read by the ECU 50 is a value shorter than the fluctuation cycle read in step 104 of the flow of FIG. Thereby, the target air-fuel ratio is controlled with a fluctuation cycle shorter than the fluctuation cycle in the first embodiment.

  Next, as in the second embodiment, it is determined whether or not the oxygen sensor output is fluctuating in synchronization with the fluctuation of the target air-fuel ratio (step 114). If it is determined in step 114 that the oxygen sensor output is fluctuating, that is, if it is determined that the catalyst is abnormally deteriorated, a check lamp provided in the vehicle is turned on (step 136). ), And the deterioration determination control is terminated (step 138). On the other hand, if it is determined in step 114 that the oxygen sensor output has not fluctuated, that is, if it is determined that the catalyst has not abnormally deteriorated, the accumulated intake air amount egasam after the start of fluctuation of the target air-fuel ratio is calculated. It is determined whether or not it is larger than the set value egasam1 (step 116). The ECU 50 reads the air amount integrated in another routine as the integrated intake air amount egasam. If it is determined in step 116 that the integrated intake air amount egasam is less than or equal to the set value egasam1, that is, it is determined that a certain amount of exhaust gas necessary to stabilize the state of the catalyst does not flow into the catalyst. In that case, the process of step 102 is executed again.

  When it is determined in step 116 that the integrated intake air amount egasam is larger than the set value egasam1, that is, when it is determined that a certain amount of exhaust gas has flowed into the catalyst, the catalyst deterioration determination control can be continued. It is determined whether or not there is (step 118). If it is determined in step 118 that the catalyst deterioration determination control cannot be continued, this control is terminated.

  If it is determined in step 118 that the catalyst deterioration determination control can be continued, it is determined whether or not the oxygen sensor output gaoxs is smaller than the reference value gaoxs0 (step 121). In this step 121, it is determined whether or not the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side. Here, since a short fluctuation period is set in step 104, an environment in which the oxygen releasing reaction hardly occurs in the catalyst is created. Therefore, normally, even in the case of a normal catalyst as well as a deteriorated catalyst, the reaction of the oxygen release reaction in the catalyst is greatly reduced, so the air-fuel ratio of the exhaust gas flowing through the catalyst becomes the fuel lean side, and the oxygen sensor output gaoxs Is smaller than the reference value gaoxs0. If it is determined in step 121 that the oxygen sensor output gaoxs is greater than or equal to the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side, the air-fuel ratio Is executed again to reverse the fuel to the fuel lean side.

  If it is determined in step 121 that the oxygen sensor output gaoxs is smaller than the deterioration determination reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side, the target Amplification of the air-fuel ratio fluctuation period eabyfrefci is started (step 160). In step 160, the ECU 50 reads the value of the amplification speed eabyfrefcu having a preset fluctuation period. By amplifying the fluctuation cycle of the target air-fuel ratio, the amount of reducing gas flowing into the catalyst 38 increases, so that an environment in which oxygen release reaction is likely to occur in the catalyst 38 is obtained.

  Next, in the same manner as in step 114, it is determined whether or not the oxygen sensor output is changing in synchronization with the change in the target air-fuel ratio (step 124). If it is determined in step 124 that the oxygen sensor output is fluctuating, that is, if it is determined that the catalyst is abnormally deteriorated, a check lamp provided in the vehicle is turned on (step 136).

  On the other hand, if it is determined in step 124 that the oxygen sensor output has not fluctuated, that is, if it is determined that the catalyst has not deteriorated abnormally, the oxygen after the amplification of the fluctuation cycle of the target air-fuel ratio has started. It is determined whether or not the sensor output gaoxs is larger than the reference value gaoxs0 (step 162). In step 162, it is determined whether or not the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side. If it is determined in step 152 that the oxygen sensor output gaoxs is less than or equal to the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is not the fuel rich side but the fuel lean side. Then, it is determined whether or not the integrated intake air amount egasam after the start of fluctuation of the target air-fuel ratio is larger than the set value egasam0 (step 128). The ECU 50 reads the air amount integrated in another routine as the integrated intake air amount egasam. In step 128, it is determined whether or not the target air-fuel ratio fluctuation period is sufficiently long until it can be determined that the catalyst has deteriorated.

If it is determined in step 128 that the integrated intake air amount egasam is equal to or less than the set value egasam0, that is, if it is determined that the fluctuation cycle of the target air-fuel ratio is not sufficiently long, the process of step 118 is executed again. To do.
On the other hand, if it is determined in step 128 that the accumulated intake air amount egasam is larger than the set value egasam0, it is determined that the fluctuation cycle of the target air-fuel ratio is sufficiently long. That is, although the fluctuation cycle of the target air-fuel ratio is sufficiently long, it is determined that the degree of deterioration of the catalyst is large because the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel lean side. In this case, without waiting until the oxygen sensor output gaoxs becomes larger than the set value gaoxs0, that is, without waiting until the air-fuel ratio of the exhaust gas flowing through the catalyst 38 changes from the fuel lean side to the fuel rich side, The provided check lamp is turned on (step 136), and the deterioration determination control is terminated (step 138).

  If it is determined in step 162 that the oxygen sensor output gaoxs is larger than the reference value gaoxs0, that is, if it is determined that the air-fuel ratio of the exhaust gas flowing through the catalyst 38 is on the fuel rich side, the target air-fuel ratio is determined. The integrated intake air amount egasum4 is calculated from the start of amplification of the fluctuation period until the oxygen sensor output gaoxs is determined to be larger than the reference value gaoxs0 (step 164). The ECU 50 can read the air amount integrated in another routine as the integrated intake air amount egasum4.

Next, referring to a map stored in advance in the ECU 50, the degree of deterioration of the catalyst corresponding to the integrated intake air amount egasum4 is calculated (step 166). In the map, the degree of catalyst deterioration is set to increase as the integrated intake air amount egasum4 increases. Thereby, the deterioration degree of the catalyst can be accurately obtained based on the integrated intake air amount egasum4.
Further, it is determined whether or not the integrated intake air amount egasum4 is larger than the catalyst deterioration determination reference value egasumn (step 168). If it is determined in step 168 that the integrated intake air amount egasum4 is larger than the catalyst deterioration determination reference value egasumn, it is determined that the catalyst is largely deteriorated. In this case, a check lamp provided in the vehicle is turned on (step 136), and then the catalyst deterioration determination control is ended (step 138).
On the other hand, if it is determined in step 168 that the integrated intake air amount egasum4 is equal to or less than the catalyst deterioration determination reference value egasumn, it is determined that the catalyst deterioration is within an allowable range. In this case, the catalyst deterioration determination control is stopped without turning on the check lamp (step 138).

  As described above, according to the routine shown in FIG. 13, the fluctuation period eabyfrefci of the target air-fuel ratio is gradually amplified to calculate the integrated intake air amount egasum4 from the start of amplification until the oxygen sensor output gaoxs is inverted. The deterioration determination of the catalyst 38 can be performed based on the calculated integrated intake air amount egasum4. Therefore, since it is not necessary to calculate the oxygen storage capacity of the catalyst, the deterioration determination of the catalyst 38 can be accurately determined. Furthermore, it is possible to accurately detect a catalyst having a high degree of deterioration.

  In the fifth embodiment, when the ECU 50 executes the processing of steps 104 and 160, the “air-fuel ratio control means” in the fifth invention executes the processing of step 164. The “intake air amount calculation means” in step 168 executes the processing of step 168, thereby realizing the “catalyst deterioration determination means” in the fifth aspect of the invention. Further, the “catalyst deterioration determining means” according to the seventh aspect of the present invention is realized by the ECU 50 executing the processing of step 166.

1 is a schematic diagram showing a configuration of an internal combustion engine system according to Embodiment 1 of the present invention. It is a conceptual diagram which shows the oxygen storage reaction and oxygen release reaction in a catalyst. It is a figure which shows the relationship between the fluctuation | variation period of a target air fuel ratio, and the oxygen sensor output after predetermined time progress from the fluctuation | variation start of a target air fuel ratio. It is a figure which shows the catalyst degradation determination method in Embodiment 1 of this invention. In Embodiment 1 of this invention, it is a flowchart which shows the catalyst deterioration determination control which ECU50 performs. It is a figure which shows the catalyst degradation determination method in Embodiment 2 of this invention. In Embodiment 2 of this invention, it is a flowchart which shows the catalyst deterioration determination control which ECU50 performs. It is a figure which shows the catalyst degradation determination method in Embodiment 3 of this invention. In Embodiment 3 of this invention, it is a flowchart which shows the catalyst deterioration determination control which ECU50 performs. It is a figure which shows the catalyst degradation determination method in Embodiment 4 of this invention. In Embodiment 4 of this invention, it is a flowchart which shows the catalyst deterioration determination control which ECU50 performs. It is a figure which shows the catalyst degradation determination method in Embodiment 5 of this invention. In Embodiment 5 of this invention, it is a flowchart which shows the catalyst deterioration determination control which ECU50 performs. It is a figure which shows the temperature change accompanying the oxygen storage reaction of a catalyst.

Explanation of symbols

2 Piston 4 Cylinder block 6 Water temperature sensor 8 Cylinder head 10 Combustion chamber 12 Spark plug 14 Intake port 16 Intake valve 18 Injector 20 Intake passage 22 Air cleaner 24 Air flow meter 26 Throttle valve 27 Throttle sensor 28 Surge tank 30 Exhaust port 32 Exhaust valve 34 Exhaust Passage 36 Air-fuel ratio sensor 38 Catalyst 40 Oxygen sensor 42 Catalyst temperature sensor 44 Crank angle sensor 46 Crankshaft 50 ECU (Electronic Control Unit)

Claims (8)

A catalyst deterioration determination device for determining deterioration of a catalyst provided in an exhaust passage of an internal combustion engine,
An exhaust gas sensor that is provided downstream of the catalyst and detects whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
The target air-fuel ratio of the exhaust gas is changed alternately between the fuel-rich side and the fuel-lean side around the fuel-rich side of the stoichiometric air-fuel ratio in a cycle shorter than the cycle in which the oxygen storage capacity of the normal catalyst fails. Air-fuel ratio control means;
Catalyst deterioration determination means for determining that the catalyst has deteriorated when the exhaust gas sensor detects that the air-fuel ratio is on the fuel lean side before a predetermined time elapses after the start of fluctuation of the target air-fuel ratio; A catalyst deterioration determination device comprising: A catalyst deterioration determination device for determining deterioration of a catalyst provided in an exhaust passage of an internal combustion engine,
An exhaust gas sensor that is provided downstream of the catalyst and detects whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
The target air-fuel ratio of the exhaust gas is changed alternately between the fuel-rich side and the fuel-lean side around the fuel-rich side of the stoichiometric air-fuel ratio in a cycle shorter than the cycle in which the oxygen storage capacity of the normal catalyst fails. a air-fuel ratio control means, the air-fuel ratio the air-fuel ratio from the start of the variation of the target air-fuel ratio when it is detected that the fuel-rich side, and gradually decreased to change the fluctuation band of the target air-fuel ratio Control means;
Even if a predetermined time elapses between the start of the change in the target air-fuel ratio and the start of the change in the change range, the catalyst is detected when the air-fuel ratio is detected to be on the fuel lean side. A determination means for determining that the deterioration has occurred;
Intake air for calculating the amount of air taken into the internal combustion engine after the change of the fluctuation range is started and until the exhaust gas sensor detects that the air-fuel ratio has changed from the fuel rich side to the fuel lean side A quantity calculation means;
A catalyst deterioration determination device, comprising: catalyst deterioration determination means for determining that the degree of deterioration of the catalyst is greater as the amount of air calculated by the intake air amount calculation means is smaller . A catalyst deterioration determination device for determining deterioration of a catalyst provided in an exhaust passage of an internal combustion engine,
An exhaust gas sensor that is provided downstream of the catalyst and detects whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
The target air-fuel ratio of the exhaust gas is changed alternately between the fuel-rich side and the fuel-lean side around the fuel-rich side of the stoichiometric air-fuel ratio in a cycle shorter than the cycle in which the oxygen storage capacity of the normal catalyst fails. Air-fuel ratio control means, wherein after changing the target air-fuel ratio by a fluctuation range in which the air-fuel ratio becomes the fuel lean side, the air-fuel ratio control means that gradually changes the fluctuation range of the target air-fuel ratio;
Intake air amount for calculating the amount of air taken into the internal combustion engine after the start of change of the fluctuation range until the exhaust gas sensor detects that the air-fuel ratio has changed from the fuel lean side to the fuel rich side Computing means;
Catalyst deterioration determination means for determining that the degree of deterioration of the catalyst is larger as the amount of air calculated by the intake air amount calculation means is larger ;
The catalyst deterioration determining means determines that the degree of deterioration of the catalyst is large when it is detected that the air-fuel ratio is on the fuel lean side even after a predetermined time has elapsed since the start of the change of the fluctuation range. A catalyst deterioration determination device, characterized in that it is configured to perform. A catalyst deterioration determination device for determining deterioration of a catalyst provided in an exhaust passage of an internal combustion engine,
An exhaust gas sensor that is provided downstream of the catalyst and detects whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
The target air-fuel ratio of the exhaust gas is changed alternately between the fuel-rich side and the fuel-lean side around the fuel-rich side of the stoichiometric air-fuel ratio in a cycle shorter than the cycle in which the oxygen storage capacity of the normal catalyst fails. a air-fuel ratio control means, the air-fuel ratio the air-fuel ratio from the start of the variation of the target air-fuel ratio when it is detected that the fuel-rich side, and gradually decreased to change the fluctuation cycle of the target air-fuel ratio Control means;
Even if a predetermined time elapses between the start of the change of the target air-fuel ratio and the start of change of the change cycle, the catalyst is detected when the air-fuel ratio is detected to be on the fuel lean side. A determination means for determining that the deterioration has occurred;
Intake air for calculating the amount of air taken into the internal combustion engine between the start of change of the fluctuation period and the time when the exhaust gas sensor detects that the air-fuel ratio has changed from the fuel rich side to the fuel lean side A quantity calculation means;
A catalyst deterioration determination device, comprising: catalyst deterioration determination means for determining that the degree of deterioration of the catalyst is greater as the amount of air calculated by the intake air amount calculation means is smaller . A catalyst deterioration determination device for determining deterioration of a catalyst provided in an exhaust passage of an internal combustion engine,
An exhaust gas sensor that is provided downstream of the catalyst and detects whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
In a period shorter than the period of the oxygen storage capacity of a normal catalyst is collapse, the target air-fuel ratio of the exhaust gas to a fuel ratio control means for varying alternately and fuel-rich side and the fuel lean side, the target air-fuel ratio Air-fuel ratio control means for gradually changing the fluctuation cycle of the target air-fuel ratio after the air-fuel ratio has been fluctuated in a fluctuation cycle on the fuel lean side ;
Intake air for calculating the amount of air sucked into the internal combustion engine after the change of the fluctuation period is started and until the exhaust gas sensor detects that the air-fuel ratio has changed from the fuel lean side to the fuel rich side A quantity calculation means;
Catalyst deterioration determination means for determining that the degree of deterioration of the catalyst is larger as the amount of air calculated by the intake air amount calculation means is larger ;
The catalyst deterioration determination means determines that the degree of deterioration of the catalyst is large when it is detected that the air-fuel ratio is on the fuel lean side even after a predetermined time has elapsed since the start of the change of the fluctuation cycle. A catalyst deterioration determination device, characterized in that it is configured to perform. In the catalyst deterioration determination apparatus according to claim 2 ,
The catalyst deterioration determining means determines that the degree of deterioration of the catalyst is small when the air-fuel ratio detected by the exhaust gas sensor is on the fuel rich side after a predetermined time has elapsed since the change of the fluctuation range was started. A catalyst deterioration determination device characterized by comprising: In the catalyst deterioration determination apparatus according to claim 4,
The catalyst deterioration determining means determines that the degree of deterioration of the catalyst is small when the air-fuel ratio detected by the exhaust gas sensor is on the fuel rich side after a predetermined time has elapsed since the change period was started. A catalyst deterioration determination device characterized by comprising: In the catalyst deterioration determination apparatus according to any one of claims 1 to 7 ,
The catalyst deterioration determination device, wherein the air-fuel ratio control means changes the target air-fuel ratio when the amount of air taken into the internal combustion engine is equal to or less than a predetermined value.

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